Your BMI is a measurement used to understand if you are at a healthy weight. It relies on your height and weight to determine whether you are:
- Underweight
- A normal weight
- Overweight
- Obese.
If you are planning on starting a weight management routine, you may want to check your BMI.
You can use an online calculator to work out your BMI. You will need to measure your height and record your weight first.
If you don’t have scales or a way to measure yourself, you can ask your local pharmacist or GP to check it for you. If you go to a gym, you might also be able to have your BMI calculated there.
Adult BMI
| Weight | Body mass index (BMI) |
|---|---|
|
Under weight
|
18.4 or lower
|
| Healthy weight |
18.5 to 24.9 |
| Over weight |
25 to 29.9 |
| Obese | 30 or higher1 |
However, it is important to note that BMI is not the only approach you can use to understand you are at a healthy weight for your gender, age, ethnicity and level of physical activity.
BMI as an indicator of health has its limitations. Where the measurement may consider different body shapes, it doesn’t account for age, muscle mass and ethnicity.
Muscle weighs more than fat. So, a professional heavyweight boxer, for example, may have a high BMI because they are very muscular. On paper, they’d be told they are overweight or obese, when they actually at a healthy weight.2
BMI is also only a suitable measure for healthy weight in people who are 20 years or older. In younger people BMI doesn’t account for the continual change in body shape as a child develops. Instead, children and young people are measured against a percentile.
Percentiles for children and young people
| Weight | Percentile |
|---|---|
|
Under weight
|
2nd percentile or below
|
| Healthy weight |
3rd to 90th |
| Over weight |
91st percentile |
| Obese | 98th percentile or higher |
BMI also doesn’t account for differences in body shape between ethnicities. It overestimates the BMI for people of Black African descent and underestimates it for people of South Asian descent. 3 For example, people from South Asia are considered obese with a BMI of 23. However, if they follow the BMI ranges above, they may not have medical intervention until their BMI is over 25, which may put them at an increased risk of type 2 diabetes and other health conditions.1,2
So, if you are calculating your BMI yourself to help with weight loss, make sure to check what a healthy range is for your age and ethnicity.
Carrying too much fat around your waist can increase your risk of heart disease, type 2 diabetes, cancer and stroke.4
Check your waist size by wrapping a tape measure around the space between the bottom of your ribs and top of your hips. Guidelines on a healthy waist size differ depending on your biological sex.
If you are male, you should try to lose weight if your waist size is 94cm (37in) or more.4
Visit your GP for support with losing weight if your waist size is 102cm (40in) or more.4
If you are female, you should try to lose weight if your waist size is 80cm (31.5in) or more.4
Visit your GP for support with losing weight if your waist size is 88cm (34.5in) or more.4
If you are from Afro-Caribbean, South-Asian, Chinese or Japanese descent, your ideal waist size will be different because your body will carry more fat and less muscle than European figures. For men your waist size should be below 90cm (35.4in) and for women it should be below 80cm (31.5in).4
Waist to hip ratio compares the size of your hip circumference (the measurement around your hips) to your waist. If your waist is bigger than your hips, you are more likely to have poor health. You should aim to have a hip to waist ratio lower than 0.85 if you’re a woman, or lower than 1 if you’re a man.5
Review date: March 2024
Next review: March 2026
Reviewed by: Mital Thakrar
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Get support and advice from your local Well pharmacist
- What is the body mass index (BMI)? nhs.uk. Published June 26, 2018. Accessed March 6, 2024. https://www.nhs.uk/common-health-questions/lifestyle/what-is-the-body-mass-index-bmi/
- Humphreys S. The unethical use of BMI in contemporary general practice. Br J Gen Pract. 2010;60(578):696-697. doi:10.3399/bjgp10X515548
- read DSJML updated 5 mins. Are BMI charts useful for children? Published August 21, 2019. Accessed March 7, 2024. https://patient.info/news-and-features/are-bmi-charts-useful-for-children
- Why your waist size matters. Accessed March 12, 2024. https://www.bhf.org.uk/informationsupport/heart-matters-magazine/medical/measuring-your-waist
- Waist to Hip Ratio | Doctor. Accessed March 12, 2024. https://patient.info/doctor/waist-to-hip-ratio
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